Profiling a camera with darktable-chart

(Hevii Guy) #21

After having recently dropped an almost-insane sum of €94 :money_mouth_face: for a small black plastic clamshell filled with a few painted colour chips, I felt that in order to gain some value for the hard-earned money spent, I had no choice but to to delve further into this and learn more to try to separate the chaff from the wheat. Not only for my own benefit but also for others who are trying to wrap their heads around this concept of camera profiling…

Umm… now it’s becoming really confusing! If the above is true, then perhaps to prevent any misunderstandings, in the same tone of the original title it would be much better to call it:

"Profiling a camera with darktable chart: Figure out how to make your RAWs look like your camera’s jpegs"

The confusion comes from having read the following:

and…

What is “most”? What is one to do if one’s conditions fall outside of this definition yet the desire is still to benefit from camera profiling? Don’t forget that the term “conditions” used in this sense can be highly subjective!
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Thank-you!
The author is to be commended for his outstanding and generous effort into producing this article. It has undoubtedly been very helpful to guide and inspire me to learn more. However, since it it now appears that the author’s primary purpose was to show how to replicate an OEM’s subjective interpretation of a “pleasing” output, others may also be left scratching their heads just as I was :face_with_head_bandage: after assuming the article implied a workflow to develop camera profiles to produce real-world results. So, in the spirit of Contribution, here’s what I’ve surmised up to this point:

Why are cameras profiled?
Three reasons:

  1. to enable the OEMs to convert Raw data into ‘pretty’ jpegs
  2. to stop beginners complaining that their favourite raw processor doesn’t produce results like the pretty jpegs regurgitated by their camera
  3. to be able to produce “accurate” results by inputting real-world colour values prior to any additional post processing tweaks, if so desired (while not forgetting the attendant critical factors of monitor and printer profiling, of course)

"But I like the OEM’s pretty jpegs"
Well then, as one of the earlier posters suggested, embrace the jpeg and be done with it! Or, if you feel adventurous, work the funky RAW further until you’re satisfied. However, there is something very important that you must keep in mind:

  • Each OEM has a different interpretation of “pretty”. In fact, pretty may even mean something all together different across the range of an OEM’s individual models.

In order to see the effect of the above, consider the following:

You and your buddy have been asked by your cousin to shoot her wedding. Somewhere you’ve heard that it’s important to “profile your camera”. As a conscientious photographer you do some research and then follow the steps found in an impressive and highly detailed article. After the wedding, when you begin to process the RAW shots taken by you and your ‘second’, you get an unsettling queasy feeling deep within the pit of your stomach: your cousin the perfectionist is going to flip because the colour of her dress isn’t the same in the various shots! That seems impossible; you took all the right steps:

  • you profiled your cameras
  • you shot in Raw
  • you even used a proper grey card (not an 18% grey) for white balancing all 4 cameras!

This is a classic apples vs oranges conundrum: Camera 1 was shooting apples, camera 2 shot oranges, camera 3 captured grapes and, finally, camera 4 recorded kumquats. Because of their OEM’s unique subjective settings, they all had different reference points which, in turn, produced different pretty results!

The only way to ensure consistency is to begin from consistency. Use a consistent reference. As far as I know, there is nothing more consistent than reality. For example, “real” colours (*let’s not get into “alternate” reality :lying_face: :wink:).
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Profiling a camera with darktable-chart: On the way to producing accurate colour results
All right, so this is what I thought that the article was going to be about! Since it wasn’t and since I’m almost certain that many others would also be interested in this, perhaps we can now move forward. In so doing, I hope that the following notes (assumptions!) might help. At the very least, they should serve as springboards for ardent collaborative discussion (vehement disagreement?), correction and consensus leading to something which we may all benefit from:

  • Shooting jpegs is unnecessary for this workflow
  • Setting proper (or ‘best’) in-camera white balance isn’t necessary since we’re only working with RAW files
  • Proper exposure is necessary(!) to prevent clipping so that all of the sample’s data can be analysed. Use an 18% grey card to adjust your camera’s exposure accordingly.
  • A set of ISO-delineated ICCs has limited effectiveness if colour accuracy is your goal. If this is indeed your goal, conduct a proper camera profiling workflow for the environment encountered in each shooting session.
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Additional Wisdom
Here are some links which may be relevant and of interest. Hopefully somebody much smarter than I am can glean some useful information within:

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(Corvus Corax) #22

I’ve seen another video using x-rite to create profile for darktable. It is here -> https://www.youtube.com/watch?v=11nInNWJHWk

I’ve followed this article and the video, but I’ve used C1 chart from http://coloraid.de/

I’ve also converted advanced input profile from RAWStudio to ICC.

I’m sure I’ve messed things up somewhere (for one, I photographed the target at a rather large angle) as I was doing for the first time and in a hurry, but profiles I’ve got from using http://coloraid.de/ are much better to what I could get with canon base curve.

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(Andreas Schneider) #23

The video is well known but contains some errors. For example the L-value he assumes for the neutral white patch is incorrect.

Good to know that the Coloraid target works great.

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(Andreas Schneider) #24

I’ve updated the article. This has quite some new information. Also if you use a ColorCheckerSG you need to use the darktable development version to create a style with darktable-chart.

New:

  • How to shoot with D50
  • How to detect glare
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(Beer Stein) #25

Newbie question: Is Darktable-chart available as a tool under Windows? I can only find references to it under Linux.

I am trying to calibrate a Plustek 7200i Slide/Negative scanner. I have an IT8 target slide. Just need to get the tool.

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#26

Hi @Beer_Stein and welcome!

I noticed that it says Avoid all windows, above, but in this case, the author does not mean Microsoft’s version…

I cannot vouch for all sources of darktable, but if you get it from here
https://www.darktable.org/install/#windows, darktable-chart is included.

Have fun!
Claes in Lund, Sweden

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(troyatlarge) #27

Hello,

I have followed the steps very carefully but run into a problem with selecting the grey ramp. I am using a basic color checker and the ColorCecker.cht for reference. However, when in process the only possible selection is A1…D6. I am guessing it should be D1…D6 as only the D row has grey squares - but maybe my understanding is incorrect. One thing for sure, its not making any photos look better at all, in fact far worse - so something is wrong somewhere - the grey ramp being my best guess as to the problem. Any help would be great - thanks

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(Mica) #28

ColorChecker.cht is for a specific color target, i’d assume, as most are for specific targets. Find the cht that matches your color target and hopefully you’ll have more success @troyatlarge

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(troyatlarge) #29

ColorChecker.cht pulls up a target that fits perfect over my chart -
all the same colors, same rows, same thing so far as I can tell. It is
the bottom row, of 4 rows (rows are A, B, C, and D), that had the gray
scale - but in the drop down menu in the process tab, it has A1…D6
as the only possible selection - as if it is saying every square in
the whole ColorChecker is suitable for the grey ramp - Im guessing
that is wrong. My guess is D1…D6 should be the the correct
selection, but no such beast in the box.

Thanks though.

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#30

Morning, @troyatlarge & welcome!

Take a look at the very first image in this thread.
Does your colour chart look like that?

If not, what chart are you using?

Have fun!
Claes in Lund, Sweden

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(Andreas Schneider) #31

@troyatlarge I had the same problem with the ColorChecker SG. In the darktable development version we changed the code to automatically detect the gray patches instead of relying a corect grey ramp definiton in the cht file.

So you either have to install the development version to get the latest darktable-chart to create a profile or wait for the release of darktable 2.6 which is normally Christmas! :slight_smile:

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(troyatlarge) #32

asn…

Ahh - thank you! You mention “…relying a correct grey ramp
definition in the cht”. Exactly what part of the cht file defines that
grey ramp? For example, mine reads, in part;

BOXES 25
F _ _ 10.0 9.75 321.25 9.75 321.26 217 10.0 217
D ALL ALL _ _ 330 228 0 0 0 0
Y 1 6 A D 46.0 46.0 12.0 11.5 52.5 52.5

Is part of this pointing to the grey ramp, and if so - which part? I
am assuming here that part of this is building the drop down box
selection in the process tab, and in this case, is doin g so
incorrectly - like it needs to be switched to Y 16 D D or some such
thing. Am I way off base here?

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(troyatlarge) #33

Claes - thank you for your reply…

No it does not look like that chart… more like the right half of that chart. It looks more like the chart seen here: https://en.wikipedia.org/wiki/ColorChecker#/media/File:Gretag-Macbeth_ColorChecker.jpg

To be exact, the chart shown is using the colors listed on the wiki page covering that color chart as seen here: https://en.wikipedia.org/wiki/ColorChecker

What we did was print out, on a high quality printer up to the task, these colors on a like shaped chart and then ran a spectral analysis on the printed colors thereby being able to calculate the DE of the colors, many of which are like 0.3, 0.5, etc., save for the white which had a DE of 3.4. I now want to test the thing for issues to see if one could reasonably use it, or if I must upload its individual Lab coordinates in its own cie file and expected XYZ in a cht file.

However, at this point I feel something else is going wrong before I even get that far - the cht file, or whatever file it is that controls it, should not have the gray ramp choice as all the rows from A1 to D6, but instead should only include D1 to D6, unless I am grossly mistaken somewhere.

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(darix) #34

If you want to give it a go you can find linux packages for the development version here:

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#35

Andreas, can you please elaborate a bit more about differences between shooting scene specific profile and general profile? How should I shoot ColorChecker Passport for scene specific lightning conditions? Are there any differences?
I find scene specific profiles very useful especially for mixed lightning fluorescent and daylight or just for artificial lightning. Market quality fluorescent bulbs and LEDs have poor spectrum and can give specific tints or color shifts.
Thank you for the article anyway! It is a great help!

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(Andreas Schneider) #36

You can create the same with a Tungten light too. However maybe this is obsolete with filmic in the meantime :slight_smile:

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#37

Sorry, I’m confused. Why filmic module obsoletes camera profiling?

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#38

Hi, I appreciate this article, as I am a photographer who uses ColorChecker to make camera profiles to use in Lightroom, but I am exploring leaving Lightroom but still want to have my cameras profiled.

I already have darktable installed and use it at a basic level, so I thought I can do this.

But it appears to be beyond me to get darktable-chart running. I am using MacOS Mojave. I eventually found a reference (not in this article) that I have to install developer version of darktable to get a working copy of darktable-chart. If this is the instruction for how to install it, link, then it is too computer-savvy-guy for me. I am more photography guy and less computer guy. I am trying to do it, but every step needs me to do things I have never done and learn things I don’t know. My computer does not even allow me to modify files like macports.conf and variants.conf, as required in the linked page.

Did I miss something, or is it really this hard to get a copy of darktable-chart and run it on my computer?

P.S. talking about an easier way, I already have the camera profiles (in .dcp format) that I made with the ColorChecker process using Macbeth target. Is there a way for me to convert these into the format needed by Darktable? Then I don’t need to do the darktable-chart process.

thanks

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#39

dcp2icc
https://sourceforge.net/projects/dcp2icc/files/

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#40

I admit I had found that, but I use MacOS.

Also, can anyone using Windows confirm that it works?

thanks

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